The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Diesel engine systems employ turbochargers to increase engine power and efficiency. Turbochargers include a turbine stage that is linked to a compressor. The turbine stage includes a turbine and receives engine exhaust gases through a turbine inlet. The exhaust gases cause the turbine to rotate at a turbine speed. The rotating turbine drives the compressor to draw in ambient air. The compressor compresses the ambient air and delivers the compressed ambient air to an intake manifold at an increased pressure called a boost pressure. Due to the increased pressure in the intake manifold, a greater mass of air enters a cylinder during an intake stroke. The greater mass of air may be mixed with a greater amount of fuel to increase engine power.
An engine controller may control the turbine speed and the boost pressure in various ways. The engine controller may decrease the turbine speed by opening a wastegate that diverts the exhaust gases away from the turbine. Alternatively, the engine controller may control vanes of a variable nozzle turbine to selectively restrict the flow of the exhaust gases through the turbine.
Turbocharger efficiency is reduced at high altitudes due to a decrease in air density. The engine controller compensates for high altitudes by increasing the turbine speed. The turbine speed is increased by increasing an exhaust pressure, which in turn increases an exhaust temperature. The increase in the exhaust temperature heats the turbine. The exhaust temperature may also increase during transient engine operations when the engine is placed under an increased load. High exhaust temperatures may damage the turbine and cause a failure of the turbocharger.